1. Technical Field
The disclosure relates generally to use of different metal-dielectric combination for controlling threshold voltages in high performance metal oxide semiconductor field effect transistor (MOSFETs).
2. Background Art
Polycrystalline silicon (Poly-Si) is widely used in the fabrication of complimentary metal oxide semiconductor (CMOS) transistors. However, continued scaling of device channels requires reduction in capacitance equivalent thickness (CET) and reduction in threshold voltages (Vt) in MOSFETs. Poly-Si as a gate material in MOSFETs presents a limitation in the reduction in CET because of dopant depletion.
To overcome the limitations of poly-Si as a gate material, one alternative is to replace poly-Si gate material with metal. The use of different combinations of metal and dielectric materials provides control over Vt where the selected gate materials dictate the work function of the gate. Poly-Si is preferred for long channel gates since it is easy to obtain Vt control, while dual metal alloy and dielectric materials for short channel CMOS devices is preferred due to a high performance requirement.